The principles of a rolling loop motion picture projector are well known and are disclosed, for example, in U.S. Pat. No. 3,494,524 (Jones) and U.S. Pat. No. 3,600,073 (Shaw), the disclosures of which are hereby incorporated by reference. Briefly, the expression "rolling loop" refers to a film transport mechanism which includes a stator and a rotor that together define a film path. The rotor is rotatable with respect to the stator and has gaps in which loops of film are progressively formed and then decay as the rotor rotates for advancing film past an aperture location. Rolling loop motion picture projectors are available commercially from Imax Corporation of Mississauga, Ontario, Canada.
IMAX.TM. rolling loop projectors are used for showing both 2-D and 3-D films. Two projectors typically are used for 3-D presentations, one for projecting "left-eye" images and the other for projecting corresponding "right-eye" images. The images may be separated using mutually extinguishing polarizers, in which case audience members wear glasses with correspondingly polarized lenses so that the viewer's left eye sees only left-eye images and the viewer's right eye sees only right-eye images.
An alternative method of stereo image separation is so-called "alternate eye" in which left eye and corresponding right eye images are projected alternately and viewers wear glasses having lenses that are alternately transmissive and non-transmissive in synchronism with the projected images. Again, the viewer's left eye sees only projected left-eye images and the viewer's right eye sees only projected right-eye images. Typically, electro-optic liquid crystal cells are used as the lenses in the glasses.
In motion picture theatres, there is a demand for variety in programming. Projector installations should be capable of allowing quick interchange between different films and films of different formats.
A 3-D IMAX.TM. theatre installation typically has two projectors, which are used together to show 3-D films or either of which can be used to show 2-D films. However, such an installation obviously requires the capital cost and maintenance cost of two projectors.
A dual rotor rolling loop projector is disclosed in U.S. Pat. No. 4,966,454 (Toporkiewicz) and can be run either with two filmstrips as a 3-D projector or a single filmstrip as a 2-D projector. However, such a projector is relatively complex and costly.
An object of the present invention is to provide a less complex form of rolling loop projector that is convertible for showing 2-D or 3-D films.